Structural element for transitory storage and deferred use of thermal energy, related structure and methods

ABSTRACT

Structural element ( 3;13 ) for a civil engineering structure, arranged for transitorily storing and using in a deferred manner thermal energy. The structural element is provided with: a first set ( 1;11 ) of at least one heat exchanger extending between a heat or coolness source (S) and the structural element so as to transfer thermal energy from the heat or coolness source to the structural element where it is transitorily stored; and a second set ( 2   a;   2   b;   12   a;   12   b ) of at least one heat exchanger extending between the structural element and at least one entity ( 5;15;17 ) external to the structural element, the second set of at least one heat exchanger being arranged for, when activated, transferring at least part of the thermal energy transitorily stored in the structural element to said entity.

The present invention relates to thermal energy management with respect to a civil engineering structure.

A civil engineering structure is conventionally provided with thermal energy by specific means, which are added to the structure precisely for that purpose. Those means include heaters when the temperature inside the structure must be increased and/or air-conditioners when the temperature inside the structure must be decreased.

More recently, it has been proposed to take benefit from the thermal energy available in an element external to the structure and to transfer it inside the structure. As an example, geothermal technique captures calories naturally stored in the soil at low depth as a result of solar energy absorption or at higher depth as a result of thermal activity of the Earth, and transforms them into a continuous and instantaneous heating solution inside e.g. a house by means of a heat pump.

Such technique may not be adapted however when the structure to be heated or cooled is not a house but a much larger civil engineering structure, such as a stadium, a building, or other. Particularly such structures are not in need of continuous heating or cooling, but only on certain occasions (e.g. matches or shows). This is because the debit flow of calories captured from the soil may then be in insufficient amount with respect to the volume to be regulated in temperature in short period of time.

Moreover, using elements external to the structure to get thermal energy may lead to the construction of a complex, heavy and costly network of geothermic probes, possibly up to long distance from the structure itself. Removal of such network would also represent a complex task.

So there is a need to improve the heating or cooling with respect to a structure, by alleviating at least in part some or all the above drawbacks.

The invention thus proposes a structural element for a civil engineering structure, arranged for transitorily storing and using in a deferred manner thermal energy. The structural element is provided with:

-   -   a first set of at least one heat exchanger extending between a         heat or coolness source and the structural element so as to         transfer thermal energy from the heat or coolness source to the         structural element where it is transitorily stored;     -   a second set of at least one heat exchanger extending between         the structural element and at least one entity external to the         structural element, the second set of at least one heat         exchanger being arranged for, when activated, transferring at         least part of the thermal energy transitorily stored in the         structural element to said entity.

Such structural element, which is (or is intended to become) part of a civil engineering structure, is the one element that stores thermal energy transitorily. The invention thus takes benefit from the structure itself to generate heat or coolness. Building a long and complex network of geothermic probes outside the structure may thus be avoided. This also helps demounting the structure if needed, as only limited portions of the heat exchangers may remain in place after removal of the structural element.

Moreover, the two different sets of heat exchangers used in cooperation with the structural element allow to bring the structural element to a determined temperature, in a process which may be continuous in time, and then, only when necessary, to use the thermal energy so transitorily stored in the structural element to increase or decrease the temperature inside the structure. Due to its thermal inertia, the structural element is thus used as a temporary heat or coolness buffer.

According to optional features that may be combined in any possible way:

-   -   the first set of at least one heat exchanger comprises at least         one tube arranged for conducting a heat transfer fluid in the         heat or coolness source, and at least one tube arranged for         conducting a heat transfer fluid in the structural element, and         wherein the second set, of at least one heat exchanger comprises         at least one tube arranged for conducting a heat transfer fluid         in the structural element;     -   the first set of at least one heat exchanger and the second set         of at least one heat exchanger have at least part of said at         least one tube arranged for conducting a heat transfer fluid in         the structural element in common;     -   the heat or coolness source (S), the structural element (3;13)         and said at least one entity (5;15;17) are separate elements;     -   the structural element is arranged so that:         -   said structural element comprises a thermal reservoir,         -   the first set of at least one heat exchanger is arranged for             transferring thermal energy from the heat or coolness source             into the thermal reservoir in the structural element, and         -   the second set of at least one heat exchanger is arranged             for transferring thermal energy between the thermal             reservoir and the at least one entity;     -   the thermal reservoir is filled at least in part with a material         capable of storing or releasing thermal energy;     -   the thermal reservoir comprises a porous material arranged to         take at least in part the lateral and vertical pressure applied         by the structure;     -   the structural element is arranged so that:         -   the first set of at least one heat exchanger comprises at             least one tube arranged for conducting a heat transfer fluid             from the heat or coolness source into the thermal reservoir,             and         -   the second set of at least one heat exchanger comprises at             least one tube arranged for conducting a heat transfer fluid             from the thermal reservoir into the structural element;     -   the first set of at least one heat exchanger and the thermal         reservoir are arranged so as to have the heat transfer fluid         circulate trough the thermal reservoir;     -   the second set of at least one heat exchanger and the thermal         reservoir are arranged so as to have the heat transfer fluid         circulate trough the thermal reservoir;     -   the structural element is arranged so that:         -   the first set (1;11) of at least one heat exchanger is             arranged for conducting a first heat transfer fluid,         -   the second set (2 a; 2 b; 12 a; 12 b) of at least one heat             exchanger is arranged for conducting a second heat transfer             fluid,         -   the thermal reservoir comprises a third heat transfer fluid,             and         -   the first set of at least one heat exchanger and the thermal             reservoir are arranged so as to have a heat transfer between             the first heat transfer fluid and the third heat transfer             fluid and the thermal reservoir and the second set of at             least one heat exchanger are arranged so as to have a heat             transfer between the third heat transfer fluid and the             second heat transfer fluid;     -   said storage space is filled at least in part with a granular         material allowing a free flow of the heat transfer fluid;     -   the heat or coolness source includes subsoil and/or an aquatic         medium such as a sea;     -   the heat or coolness source is a heat source and includes a set         of at least one solar probe;     -   said at least one entity includes another structural element for         the civil engineering structure and/or air adjacent to the         structural element;     -   the second set of at least one heat exchanger is arranged at         least in part for conducting air throughout the structural         element;     -   the first and/or second set of at least one heat exchanger makes         use of at least one (simple) pump;     -   the first and/or second set of at least one heat exchanger makes         use of at least one heat pump;     -   the structural element is at least in part made of backfill         stabilized using at least one reinforcement member within the         structural element;     -   at least one reinforcement member is connected to a facing that         marks a boundary for the structural element, the facing being         possibly separated from the backfill by at least one location         with a thermal insulation material such as expanded polystyrene         or mineral fibres;     -   at least one heat exchanger of the first and/or the second set         of at least one heat exchanger is connected to the facing;     -   the structural element is arranged for being part of one of the         following civil engineering structures: a stadium structure and         a greenhouse; and/or     -   the structural element is arranged for supporting benches and         possibly a playing field and said at least one entity includes         the benches and/or air adjacent to the benches.

The invention also proposes a civil engineering structure comprising at least one structural element for transitorily storing and using in a deferred manner thermal energy as mentioned above, such as a stadium structure.

The invention also proposes a method for transitorily storing and using in a deferred manner thermal energy in a structural element as mentioned above. This method comprises:

-   -   maintaining active a first set of at least one heat exchanger         extending between a heat or coolness source and the structural         element so as to transfer thermal energy from the heat or         coolness source to the structural element where it is         transitorily stored;     -   when a determined criterion is satisfied, activating a second         set of at least one heat exchanger extending between the         structural element and at least one entity external to the         structural element, the second set of at least one heat         exchanger being arranged for transferring at least part of the         thermal energy transitorily stored in the structural element to         said entity.

The invention also proposes a method for building a structural element for transitorily storing and using in a deferred manner thermal energy as mentioned above. This method comprises:

-   -   providing a first set of at least one heat exchanger with a         first end extending from a heat or coolness source;     -   building, in successive lifts, a structural element for it to         cover a second end of each heat exchanger of said first set;     -   alternately with the building of the successive lifts of the         structural element, placing a second set of at least one heat         exchanger, so that a first end of each heat exchanger of said         second set is surrounded by the structural element while a         second end of each heat exchanger of said second set extends to         at least one entity external to the structural element.

The preferred features of the above aspects which are indicated by the dependent claims may be combined as appropriate, and may be combined with any of the above aspects of the invention, as would be apparent to a person skilled in the art.

FIG. 1 is a schematic sectional elevation view of an exemplary structural element for a civil engineering structure provided with an exemplary first set of heat exchangers;

FIG. 2 is a schematic sectional top view of heat exchangers used in the exemplary structural element of FIG. 1 according to II-II;

FIG. 3 is a schematic sectional elevation view of an exemplary structural element for a civil engineering structure provided with an exemplary second set of heat exchangers;

FIG. 4 is a schematic sectional elevation view of an exemplary structural element for a civil engineering structure provided with another exemplary second set of heat exchangers;

FIG. 5 is a schematic sectional elevation view of an exemplary structural element provided with additional elements;

FIG. 6 is a schematic sectional elevation view of an exemplary structural element which is part of a stadium;

FIG. 7 is a schematic sectional elevation view of an exemplary structural element for a civil engineering structure provided with an exemplary set of heat exchangers and a thermal reservoir according to embodiment of the invention;

FIG. 8 is a schematic sectional elevation view of an exemplary structural element for a civil engineering structure provided with an exemplary set of heat exchangers and a thermal reservoir according to another embodiment of the invention.

An aspect of the present invention relates to a structural element for a civil engineering structure. Any structural element for any type of engineering structure may be envisaged. In the following, an element for a stadium structure will be more particularly considered, without limiting in any way the general scope of the invention. Other examples of structures to which the invention may apply include e.g. a greenhouse, a building, and/or other.

FIG. 1 thus shows a structural element 3 for a stadium in the form of a backfill intended to support benches and possibly to be adjacent to a playing field.

Such structural element 3 can be made of any type of natural and/or artificial material. As an example, it may comprise soil or earth, possibly stabilized. Alternatively or in addition, it may comprise concrete, possibly recycled, steel and/or other.

The structural element 3 is arranged for transitorily storing and using in a deferred manner thermal energy, i.e. heat or coolness.

To do so, the structural element 3 is provided with two different sets of at least one heat exchanger each.

FIG. 1 shows a first set 1 of heat exchangers. Those heat exchangers extend between a heat or coolness source S and the structural element 3.

In the illustrated example, the heat or coolness source S includes subsoil above which the structural element 3 is located. Alternatively or in addition, the heat or coolness source S may include other subsoil, e.g. located further away and/or not below the structural element 3. Alternatively or in addition, the heat or coolness source S may include an aquatic medium such as a sea, groundwater and/or other, in which an end of the heat exchangers of the first set 1 are immersed.

Other variants for the heat or coolness source S may be envisaged alternatively or in addition, as will be apparent to one skilled in the art. In an advantageous example, S may be a heat source and include a set of at least one solar probe, so as to take benefit from the heat generated from the sun.

Note that different sources may be used depending on whether heat or coolness is sought. Alternatively, a single source may be used as a heat source or a coolness source, depending e.g. on the external temperature. For instance, the subsoil S lying below the structural element 3 may be used as a heat source in winter when the air temperature is low, while it may be used as a coolness source in summer when the air temperature is high.

In the example of FIG. 1, the first set 1 of heat exchangers consists of tubes including any type of heat transfer fluid, such as water and/or other, and divided into two main parts. The bottom part of the heat exchangers comprises a vertical portion of the tubes, while the top part of the heat exchangers comprises a horizontal portion of the tubes.

In the bottom part, the tubes may be closed so that the heat exchangers work in closed loop. This is adapted for example when the heat or coolness source S consists in subsoil. Alternatively, the tubes may be open so that the heat exchangers work in open loop. This is adapted for example when the heat or coolness source S includes an aquatic medium. In the bottom part, the tubes may be substantially parallel and/or of similar length as represented in FIG. 1.

In the top part, the heat exchangers of the first set 1 may be closed. They may be arranged in superposed layers as represented in FIG. 1. They may be included in substantially horizontal planes respectively. Alternatively or in addition, each layer of heat exchangers may include several branches, as shown in the top view of FIG. 2.

Note that the geometry of the first set 1 of heat exchangers may take various forms and the above-described example should be in no way interpreted as limiting. For example, the heat exchangers may not be vertical and/or parallel in their bottom part. They may not be horizontal and/or parallel in their top part. Also, they may not have two different portions. As another non-limiting example, the first set 1 of heat exchangers could consist only in a series of vertical tubes extending from the subsoil S into the structural element 3. At least some of the heat exchangers of the first set 1 may not have a rectilinear course.

At least some of the first set 1 of heat exchangers may be located at least in part in the foundation of the civil engineering structure, e.g. the stadium, in which it is intended to cooperate.

In any case, thermal energy is transferred by means of the first set 1 of heat exchangers from the heat or coolness source S to the structural element 3 where it is transitorily stored.

This transfer may result from natural circulation of a heat transfer fluid within the heat exchangers of the first set 1.

Advantageously, the first set 1 of heat exchangers may make use of an additional device 4 to facilitate the thermal energy transfer as shown in FIG. 1. This device 4 may comprise at least one simple pump which favours circulation of a heat transfer fluid within the heat exchangers, thereby increasing the heat exchanges between the heat or coolness source S and the structural element 3, as will be easily understood by one skilled in the art.

Alternatively or in addition, the device 4 may comprise at least one heat pump. Such heat pump, which may comprise at least a condenser, an expansion valve, an evaporator and a compressor as is conventional, has the effect of offsetting the temperature in the first set 1 of heat exchangers and the temperature in the heat or coolness source S, as will be easily understood by one skilled in the art. Compared to a simple pump, the use of a heat pump allows increasing the heat exchanges between the heat or coolness source S and the structural element 3. The structural element 3 can thus be made colder or hotter depending on the sought result.

Note that the position and the number of simple pump(s) and/or heat pump(s) may be various and different from the example shown for illustrative purpose in FIGS. 1 and 2.

In the attached figures, hot and cold portions of the heat exchangers have been schematically represented with thick and thin lines respectively. It should be understood however that this representation is only for illustrating the direction of the transfer of thermal energy, and should not be interpreted as a strict delimitation.

In the example shown in FIG. 1, which corresponds more particularly to a process of cooling of the structural element 3 and a coincident heating of a coolness source S, it can be seen that the first set 1 of heat exchangers is used to direct coolness from the coolness source S to the structural element 3 and, coincidently, to direct heat from the structural element 3 to the coolness source S. The thermal energy transfer would be in the opposite direction should the structural element 3 be heated by means of a heat source S and via the first set 1 of heat exchangers.

The first set 1 of heat exchangers may be maintained active on a determined period of time, which may be long, such as several days, weeks or months. It may be maintained active continuously or quasi-continuously. This may ensure that the structural element 3 reaches a determined temperature and stores a determined amount of thermal energy.

The thermal energy so transitorily stored within the structural element 3, and thus within the civil engineering structure in which the structural element 3 takes part, will then be transferred at least in part to at least one entity external to the structural element 3.

The entity in question may include another structural element for the civil engineering structure in which the structural element 3 takes part. For example, when talking of a stadium structure, the entity may include benches. Alternatively or in addition, the entity may include air adjacent to the structural element 3. For example, when talking of a stadium structure, the entity may include air adjacent to benches which are supported by the structural element 3, or more generally air located at or around the center of the stadium. Many other types of entities may be envisaged, depending on the application, as will be apparent to one skilled in the art.

Transferring at least part of the thermal energy transitorily stored in the structural element 3 to at least one entity is made by activating a second set of at least one heat exchanger extending between the structural element 3 and said entity.

The activation of the second set of at least one heat exchanger may result from the fact that a determined criterion is satisfied. Any possible criterion may be envisaged in this regard. As an example, the criterion may be related to the usage of the civil engineering structure in which the structural element 3 takes part. When talking of a stadium, such criterion may include the immediate or coming (e.g. in a few hours) start of a match game. Other occasions, such as shows, periodical events, and/or other may also be the basis for a determined criterion being satisfied. Dynamic parameters such as temperatures, e.g. of the air, of the structural element 3, of the entity and/or of other element(s), may be taken into account in the considered criterion.

The detection of a determined criterion being satisfied and/or the resulting activation of the second set of at least one heat exchanger may be totally automatic, totally manual or a combination of automatic and manual operations.

Because the thermal energy transitorily stored in the structural element 3 is transferred at least partly to the entity only upon activation of the second set of at least one heat exchanger, that is possibly long after it has started being stored in the structural element 3, it may be seen as a deferred use of such thermal energy. This is contrast with prior techniques, in which only one set of heat exchangers is needed and/or the thermal energy obtained via this set is used directly and without delay.

FIGS. 3 and 4 show two examples of a second set of at least one heat exchanger that may be each used to transfer at least part of the thermal energy transitorily stored in the structural element 3 to a respective entity. Those two examples may be carried out alone or together. In those examples, it is assumed that coolness was transitorily stored in the structural element 3 as a result of the above-described action of the first set 1 of at least one heat exchanger, and that at least part of that coolness is to be transferred through said second set(s) of at least one heat exchanger. But it will be understood that the same type of arrangement may be used to take benefit from heat transitorily stored in the structural element 3.

In the example of FIG. 3, the second set 2 a of heat exchangers is arranged at least in part for conducting air throughout the structural element 3. To this end, it includes at least one inlet for hot ambient air (on the left end of the structural element 3 on FIG. 3) and at least one outlet for refreshed air (several outlets on the right end of the structural element 3 on FIG. 3).

In this case, the incoming air is conducted from outside the structural element 3 into the heat exchangers of the second set 2 a and throughout the structural element 3. It is thus refreshed by contact of the heat exchangers with the structural element 3 storing coolness. The refreshed air leaves the heat exchangers of the second set 2 a and it mixes hot ambient air adjacent to the structural element 3.

In order to be conducted within the heat exchangers of the second set 2 a and throughout the structural element 3, the air may be pulsed with conventional pulsing means, such as fans. Alternatively or in addition, the air may be simply sucked by a natural convective air flow organized within the civil engineering structure. In case of a stadium, the air may indeed flow from the outside to the inside of the stadium, e.g. by escaping through a hole in the roof of the stadium.

By virtue of such arrangement, spectators sitting on benches and/or players standing on a playing field of the stadium may be refreshed, as they receive refreshed air.

As shown in FIG. 3, devices 9 may be placed at the exit of some or all of heat exchangers of the second set 2 a so as to regulate the ventilation flow to a desired intensity. Those devices 9 may be used to activate or deactivate the second set 2 a of heat exchangers.

In the example of FIG. 4, the second set 2 b of heat exchangers extends between the structural element 3 and benches supported by the structural element 3. Alternatively or in addition, it may also extend between the structural element 3 and an adjacent playing field.

The second set 2 b of heat exchangers may include tubes filled with a heat transfer fluid, e.g. in closed loop.

Like for the first set 1 of heat exchangers mentioned above, one or several simple pumps or heat pumps 10 may be used to favour the heat exchanges between the structural element 3 and the benches (or any other suitable entity). Those pumps 10 may be used to activate or deactivate the second set 2 b of heat exchangers.

With this arrangement, spectators sitting on the benches supported by the structural element 3 and/or players standing on a playing field adjacent to the structural element 3 may be refreshed by contact or proximity with the refreshed benches and/or playing field.

In FIGS. 3 and 4, the second sets of heat exchangers have been represented in superposed and substantially horizontal layers. However, as mentioned above with respect to the first set 1 of heat exchangers, any other appropriate geometry may apply for the second set(s) of heat exchanger(s), as will be apparent to one skilled in the art. As an example, at least some heat exchangers of the second set(s) may be independent. As another example, a non-rectilinear course, e.g. a wavy course, may be envisaged for at least some of the heat exchangers of the second set(s).

FIG. 5 shows an exemplary arrangement for a structural element 3 which may be provided with first and second sets of least one heat exchanger as mentioned above.

This structural element 3 of FIG. 5 is at least in part made of a backfill, which is advantageously stabilized by means of at least one (unrepresented) reinforcement member within the structural element 3. It may for example consist in conventional stabilized and possibly compacted soil or earth. A conventional technique of the Reinforced Earth® company, or similar techniques, may be used in this regard.

As shown in FIG. 5, a facing 6 may mark a boundary for the backfill.

Moreover, one or several reinforcement members extending within the backfill may be connected to this facing. Alternatively or in addition, one or several reinforcement members may be disconnected from this facing. The reinforcement members may take various forms and use various materials, such as metal (for example galvanized steel), synthetic (for example based on polyester fibers), a combination thereof, etc. They may be placed in the backfill with a density that is dependent on the stresses that might be exerted on the structure, as will be apparent to one skilled in the art.

The facing 6 may be made of prefabricated concrete elements, e.g. in the form of slabs or blocks, juxtaposed to cover the front face of the structure. It may be built in situ by pouring concrete or a special cement.

Advantageously, the facing 6 may be separated from the backfill by at least one location (and possibly on all its internal surface) with a thermal insulation material 7 such as expanded polystyrene, mineral fibres and/or other. By doing so, it is avoided that too much of the thermal energy transitorily stored in the structural element 3 escapes through the facing 6. When heat exchangers must go out of the structural element, corresponding limited holes may be arranged in the facing 6 and the insulation material 7 for this purpose.

In an advantageous arrangement, at least part of the first and/or second set of at least one heat exchanger may simultaneously play the role of reinforcement member(s) for the stabilized structural element 3. In this case, at least one heat exchanger of the first and/or second set of at least one heat exchanger may be connected to the facing 6. In particular, horizontal parts of heat exchangers of the first set 1 and/or the second set 2 a-2 b as described above may be additionally used as reinforcement members for the stabilized structural element 3. It is thus avoided to provide heat exchangers and reinforcement members independently, which reduces both the time required to build the structure and its cost.

When the structural element 3 is part of stadium, as assumed above, benches 5 may mark another boundary thereof, opposite to the facing 6. Such benches 5 may have the same composition as the structural element 3, for example stabilized soil or earth. Alternatively or in addition, the benches 5 may use different materials, such as wood, cement, concrete and/or other.

Various elements may be placed at least partly on or in the structural element 3. For example, access stairs, tiers and/or railings may be placed on the backfill. Cubicles, technical premises, access tunnels and/or shops may be placed inside the backfill. Those elements could be cooled or heated as desired, by means of the above-described first and/or second set of at least one heat exchanger.

As shown in FIG. 5, a cover 8 may be laid or bridged over the backfill. This cover might act as a roofing to prevent ingress of rain water or might be airproof.

Many other arrangements for a structural element may be envisaged within the framework of the present invention, as will be apparent to one skilled in the art.

FIG. 6 shows a portion of a stadium structure including an exemplary structural element 13 which may be identical or similar to the structural element 3 described above. This structural element 13 is provided with:

-   -   a set 11 of heat exchangers possibly associated with simple or         heat pumps 14, which may identical or similar to the first set 1         of at least one heat exchanger described above (here vertical         and separate heat exchangers are represented);     -   a set 12 a of heat exchangers, which may identical or similar to         the second set 2 a of at least one heat exchanger described         above (here wavy and separate heat exchangers going throughout         the structural element 3 are represented);     -   a set 12 b of heat exchangers possibly associated with simple or         heat pumps 20, which may identical or similar to the second set         2 b of at least one heat exchanger described above;     -   a facing 16 which may identical or similar to the facing 6         described above.

Other elements may be associated with the structural element 13. For example, benches 15 are supported by the structural element 13. A playing field 17 is located next to the structural element 13. Reinforcements may be placed within the structural element 13, etc.

According to an embodiment, the first set 11 of heat exchanger corresponds to the one described previously, in particular said first set of heat exchanger comprises a tube arranged for conducting a heat transfer fluid in the heat or coolness source and a tube arranged for conducting a heat transfer fluid in the structural element 13.

The second set of heat exchanger may also comprise a tube arranged for conducting a heat transfer fluid in the structural element 13.

According to a particular embodiment of the invention, the first and second sets of heat exchangers have part of said tube arranged for conducting a heat transfer fluid in the structural element in common.

FIGS. 7 and 8 show a portion of a structural element 13 according to embodiments of the invention. According to theses embodiments, the structural element 13 comprises a thermal reservoir 30, a first set of heat exchanger comprising tubes 31 arranged for conducting a first heat transfer fluid and a second set of heat exchanger comprising tubes 32 arranged for conducting a second heat transfer fluid.

In the embodiment represented on FIG. 7, the first and second heat exchangers comprise tubes that are arranged so as to circulate trough in the thermal reservoir 30.

According to such embodiments of the invention, the heat exchanger may be arranged in layers, for example they may be included in substantially horizontal or vertical planes respectively. Alternatively or in addition, each heat exchanger may include several branches.

The geometry of the heat exchangers may take various forms and the above-described examples should be in no way interpreted as limiting. For example, the heat exchangers may not be vertical and/or parallel. They may not be horizontal and/or parallel. Also, they may not have two different portions. At least some of the heat exchangers of the first and second sets may not have a rectilinear course.

The thermal reservoir 30 is arranged so as to be able to take the lateral and vertical pressure applied by the structure and store and release thermal energy. For example the thermal reservoir 30 may be delimited by a liner filed with soil, earth, sand or rocks.

The tubes of the first and second heat exchanger are closed so that the heat exchangers work in closed loop.

For example, the first heat exchanger may have a hot fluid circulate trough the tubes of the first heat exchanger in the thermal reservoir so as to heat up the material comprised in the thermal reservoir. According to this embodiment, the heat transfer fluid remains in the tubes and does not come in contact with the material comprised in the thermal reservoir.

When required one may have a second heat transfer fluid circulate in the tubes of the second heat exchanger in the thermal reservoir. The second heat transfer fluid is heated by the porous material trough the tubes.

According to such embodiment, no fluid exchange takes place between the first and second heat exchanger and the thermal reservoir. Such heat transfer may also apply with a cold source.

Advantageously, the structure element 13 according to the embodiment of FIG. 7 presents a high thermal inertia, allowing to release slowly the thermal energy stored in the thermal reservoir.

According to the embodiment represented on FIG. 8., the thermal reservoir 30 is filed with a porous material arranged so as to be able to take the lateral and vertical pressure applied by the structure. For example the thermal reservoir 30 may be filed with soil or earth or stones or gravel or rocks.

A good porous material should be strong, hard-wearing, stable, drainable, resistant to deformation, easily available, and reasonably cheap to purchase.

For example the porous material is made of crushed natural rock with particles between 28 mm and 50 mm in diameter. A high proportion of particles finer than this would reduce its drainage properties, and a high proportion of larger particles would result in the load being distributed improperly. Angular stones are preferable to naturally rounded ones, as angular stones interlock with each other.

Granite is one of the best materials in this regard. It is also possible to use the slag produced by blast furnaces. In generally material used for track ballast is suitable as porous material.

The tubes of the first and second heat exchangers are open so as to have the heat transfer fluid circulate trough the thermal reservoir trough the porous material.

For example, the first heat exchanger may have a hot fluid circulate trough the thermal reservoir so as to heat up the porous material comprised in the thermal reservoir.

When required one may have a second heat transfer fluid circulate trough the thermal reservoir using the second heat exchanger. The second heat transfer fluid being heated by the porous material.

Such heat transfer may also apply with a cold source.

Advantageously, the structure element 13 according to the embodiment of FIG. 8 presents a high thermal exchange rate between the porous material and the heat exchange fluids circulating trough the porous material comprised in the reservoir.

One skilled in the art will appreciate that other arrangements may be envisaged. Those arrangements may be adapted depending on the nature and usage of the civil engineering structure considered.

Building the structural element 3 or 13 described above may be performed by:

-   -   providing the first set 1 or 11 of at least one heat exchanger         with a first end extending from the heat or coolness source S.         With respect to the examples described above, this may come to         positioning the bottom part of the heat exchangers of the first         set 1 or 11 in a subsoil or aquatic medium, while their top part         would be kept above;     -   building, in successive lifts, the structural element 3 or 13         for it to cover a second end of each heat exchanger of said         first set 1 or 11. At the end of this operation, the first set 1         or 11 is fully covered by the structural element 3 or 13;     -   alternately with the building of the successive lifts (or         layers) of the structural element 3 or 13, placing a second set         2 a, 2 b, 12 a and/or 12 b of at least one heat exchanger, so         that a first end of each heat exchanger of said second set is         surrounded by the structural element 3 or 13 while a second end         of each heat exchanger of said second set extends to at least         one entity external to the structural element. For example, a         first lift of structural element may be placed on the ground and         then at least one first heat exchanger of the second set may be         put on this first lift. This step may be repeated until all the         heat exchangers of the second set are put in place. Finally, the         top part of the second set of at least one heat exchanger is         covered by the last lift of structural element. The second set,         just like the first set, is finally fully surrounded by the         structural element.

Other buildings methods may be carried out alternatively or in addition, as will be apparent to one skilled in the art.

Note that demounting or removing such structural element 3 or 13 is not too complex a task. For example, when the structural element is mainly made of earth, the latter may be taken away little by little. The heat exchangers of the second set and possibly of the first set (and/or other elements), cleared by this operation, may be removed in turn. Most or all of those elements may be reused later on to build a new structure at the same location or elsewhere. 

1. A structural element for a civil engineering structure, arranged for transitorily storing and using in a deferred manner thermal energy, the structural element having: a first set of at least one heat exchanger extending between a heat or coolness source and the structural element so as to transfer thermal energy from the heat or coolness source to the structural element where it is transitorily stored; a second set of at least one heat exchanger extending between the structural element and at least one entity external to the structural element, the second set of at least one heat exchanger being arranged for, when activated, transferring at least part of the thermal energy transitorily stored in the structural element to said entity.
 2. The structural element as claimed in claim 1, wherein the first set of at least one heat exchanger comprises at least one tube arranged for conducting a heat transfer fluid in the heat or coolness source and at least one tube arranged for conducting a heat transfer fluid in the structural element, and wherein the second set of at least one heat exchanger comprises at least one tube arranged for conducting a heat transfer fluid in the structural element.
 3. The structural element as claimed in claim 2, wherein the first set of at least one heat exchanger and the second set of at least one heat exchanger have at least part of said at least one tube arranged for conducting a heat transfer fluid in the structural element in common.
 4. The structural element as claimed in any one of the foregoing claims, wherein the heat or coolness source, the structural element and said at least one entity are separate elements.
 5. The structural element as claimed in any one of the foregoing claims, wherein said structural element comprises a thermal reservoir, the first set of at least one heat exchanger is arranged for transferring thermal energy from the heat or coolness source into the thermal reservoir in the structural element, the second set of at least one heat exchanger is arranged for transferring thermal energy between the thermal reservoir and the at least one entity.
 6. The structural element as claimed in claim 5, wherein the thermal reservoir is filled at least in part with a material capable of storing or releasing thermal energy.
 7. The structural element as claimed in claim 5, wherein the thermal reservoir comprises a porous material arranged to take at least in part the lateral and vertical pressure applied by the structure.
 8. The structural element as claimed in claim 5, wherein the first set of at least one heat exchanger comprises at least one tube arranged for conducting a heat transfer fluid from the heat or coolness source into the thermal reservoir, and the second set of at least one heat exchanger comprises at least one tube arranged for conducting a heat transfer fluid from the thermal reservoir into the structural element.
 9. The structural element as claimed in claim 8, wherein the first set of at least one heat exchanger and the thermal reservoir are arranged so as to have the heat transfer fluid circulate through the thermal reservoir.
 10. The structural element as claimed in claim 8, wherein the second set of at least one heat exchanger and the thermal reservoir are arranged so as to have the heat transfer fluid circulate through the thermal reservoir.
 11. The structural element as claimed in claim 8, wherein the first set of at least one heat exchanger is arranged for conducting a first heat transfer fluid, the second set of at least one heat exchanger is arranged for conducting a second heat transfer fluid, the thermal reservoir comprises a third heat transfer fluid, and wherein the first set of at least one heat exchanger and the thermal reservoir are arranged so as to have a heat transfer between the first heat transfer fluid and the third heat transfer fluid and the thermal reservoir and the second set of at least one heat exchanger are arranged so as to have a heat transfer between the third heat transfer fluid and the second heat transfer fluid.
 12. The structural element as claimed in any one of the foregoing claims, wherein the heat or coolness source includes subsoil and/or an aquatic medium.
 13. The structural element as claimed in claim 1, wherein the heat or coolness source is a heat source and includes a set of at least one solar probe.
 14. The structural element as claimed in claim 1, wherein said at least one entity includes another structural element for the civil engineering structure and/or air adjacent to the structural element.
 15. The structural element as claimed in claim 1, wherein the second set of at least one heat exchanger is arranged at least in part for conducting air throughout the structural element.
 16. The structural element as claimed in claim 1, wherein the first and/or second set of at least one heat exchanger makes use of at least one pump.
 17. The structural element as claimed in claim 1, wherein the first and/or second set of at least one heat exchanger makes use of at least one heat pump.
 18. The structural element as claimed in claim 1, wherein the structural element is at least in part made of backfill.
 19. The structural element as claimed in claim 18, wherein the backfill is stabilized using at least one reinforcement member within the structural element.
 20. The structural element as claimed in claim 18, wherein at least one reinforcement member is connected to a facing forming a boundary for the structural element.
 21. The structural element as claimed in claim 19, wherein at least one heat exchanger of the first and/or the second set of at least one heat exchanger is connected to the facing.
 22. The structural element as claimed in claim 1, wherein the civil engineering structure comprises a stadium structure or a greenhouse.
 23. The structural element as claimed in claim 22, wherein the structural element is arranged for supporting benches and/or a playing field in a stadium.
 24. A civil engineering structure comprising at least one structural element for transitorily storing and using in a deferred manner thermal energy, wherein the structural element comprises: a first set of at least one heat exchanger extending between a heat or coolness source and the structural element so as to transfer thermal energy from the heat or coolness source to the structural element where it is transitorily stored; a second set of at least one heat exchanger extending between the structural element and at least one entity external to the structural element, the second set of at least one heat exchanger being arranged for, when activated, transferring at least part of the thermal energy transitorily stored in the structural element to said entity.
 25. A method for transitorily storing and using in a deferred manner thermal energy in a structural element, the method comprising: maintaining active a first set of at least one heat exchanger extending between a heat or coolness source and the structural element so as to transfer thermal energy from the heat or coolness source to the structural element where it is transitorily stored; when a determined criterion is satisfied, activating a second set of at least one heat exchanger extending between the structural element and at least one entity external to the structural element, the second set of at least one heat exchanger being arranged for transferring at least part of the thermal energy transitorily stored in the structural element to said entity.
 26. A method for building a structural element for transitorily storing and using in a deferred manner thermal energy, the method comprising: providing a first set of at least one heat exchanger with a first end extending from a heat or coolness source; building, in successive lifts, a structural element for it to cover a second end of each heat exchanger of said first set; alternately with the building of the successive lifts of the structural element, placing a second set of at least one heat exchanger, so that a first end of each heat exchanger of said second set is surrounded by the structural element while a second end of each heat exchanger of said second set extends to at least one entity external to the structural element.
 27. The structural element as claimed in claim 20, wherein the facing is separated from the backfill at least at one location with a thermal insulation material.
 28. The structural element as claimed in claim 27, wherein the thermal insulation material comprises expanded polystyrene or mineral fibres.
 29. The civil engineering structure as claimed in claim 24, embodied as a stadium structure. 